Activator for cyanoacrylate adhesives

ABSTRACT

An activator for cyanoacrylate adhesives based on N,N-dialkyl aniline derivatives is provided. The activators are characterized by a molecular weight of more than 200 and by at most 3 carbon atoms for both N,N-dialkyl substituents together. Also provided are methods of production and use of the activator and to the combination product of the activator and the cyanoacrylate adhesive.

This application is a divisional application of U.S. Ser. No. 08/133,152filed 12 Oct. 1993 now U.S. Pat. No. 5,428,115.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an activator for cyanoacrylate adhesives basedon N,N-dialkyl aniline derivatives, to its production and use and to thecombination product of the activator and the cyanoacrylate adhesive.

An "activator" is generally understood to be an accelerator usedseparately to cure a chemically reacting one-component adhesive. In thepresent case, the polymerization of 2-cyanoacrylates in particular isactivated.

2. Discussion of Related Art

Activators as defined above are known. Thus, DE-OS 24 13 406 describesparticles of a porous support impregnated with anN,N-dialkyl-substituted aniline containing 1 to 4 carbon atoms in thealkyl radical for initiating the delayed polymerization of monomericcyanoacrylates. The delay is brought about by the porous supports. TheN,N-dialkyl-substituted anilines used include N,N-dimethyl aniline,N,N,2,4-tetramethyl aniline, N,N,3,5-tetramethyl aniline,N,N-dimethyl-o-toluidine, N,N-dimethyl-m-toluidine,N,N-dimethyl-p-toluidine, N-methyl-N-phenylbenzyl amine and/or theircorresponding N-ethyl and N,N-diethyl derivatives.

N,N-Dimethyl-p-toluidine is preferred. The adhesive bonds obtained arenot transparent. The invention is intended for the field of dentalmedicine. The disadvantage that N,N-dimethyl toluidine is toxic and hasan unpleasant odor is particularly serious in this case.

Accordingly, there has been no shortage of attempts to use less toxicactivators. In Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 19(2),pages 585-90, aniline derivatives were investigated both from thisviewpoint and for cure time, strength and color stability. BesidesN,N-dimethyl toluidine and xylidine, 4-N,N-dimethylaminobenzaldehyde andbenzoic acid and methyl esters thereof were among the anilinederivatives investigated. Although these compounds may be less toxic,they are still unsuitable for use as activators because they activatefar too weakly, if at all. Other activators rapidly form a skin withsubsequent slow curing when solutions thereof are sprayed onto amonomeric cyanoacrylate layer. The shock-like curing at the surfaceresults in a wrinkled structure which, in addition, destroystransparency in most cases.

Accordingly, N,N-dimethyl toluidine remains the only effective activatorfor cyanoacrylates. Since it is classified as a "T substance" under thelegislation on chemicals, this activator has to be used in aconcentration of more than 1%. Further disadvantages of the knownactivator are its volatility, which releases DMT even after bonding, andthe unpleasant odor associated therewith.

Accordingly, the problem addressed by the present invention was toremedy this situation by providing an activator which would have few, ifany, of these disadvantages and which would be better in its handlingand performance properties than known activators, particularly in regardto the balance between transparency, odor, toxicity, curing behavior,strength and surface structure.

DESCRIPTION OF THE INVENTION

The solution provided by the invention is defined in the claims. It liesin the choice of certain tertiary aniline derivatives of which themolecular weight plays a crucial part. It should be above 200 and ispreferably above 600. In the context of the invention, the molecularweight is an average value derived from the stoichiometry of thereaction mixtures.

"Based on" means that the activator is largely built up on the effect ofthe aniline derivatives according to the invention. In addition, it mayalso contain inert liquids or solids.

The dialkyl aniline derivatives according to the invention are usedmainly in the form of a solution in organic solvents. However, not onlyshould the solvent dissolve the dialkyl aniline derivatives according tothe invention, it should also be soluble in the monomeric cyanoacrylate.In addition, it should be inert to the dialkyl aniline derivativesaccording to the invention and should readily evaporate at roomtemperature. Suitable solvents are ketones, such as acetone and methylethyl ketone; esters, such as ethyl, propyl or butyl acetate;chlorinated hydrocarbons, such as methylene chloride or1,1,1-trichloroethane; aromatic hydrocarbons, such as toluene; andaliphatic hydrocarbons, such as n-heptane. The dialkyl anilinederivatives according to the invention are best dissolved in aconcentration of 0.1 to 5% by weight and preferably in a concentrationof 0.5 to 2% by weight.

In addition, the solution may contain other substances, for example dyesor optical brighteners, to enable its application to be bettercontrolled.

The solutions containing the aniline derivatives according to theinvention may be applied to the surfaces to be treated in finelydispersed form by immersion, spraying, spreading or any other suitablemethod. They may be applied to the parts to be joined both before andafter the cyanoacrylate adhesive. An activator is preferably appliedbefore or afterwards.

In one advantageous embodiment, however, the activator according to theinvention may also be mixed with powder to form a paste which, aftermixing with cyanoacrylate adhesive, may be used to seal gaps or to fillcavities.

In the dialkyl aniline derivatives according to the invention, thedialkyl aniline group preferably forms a terminal group of oligomers orpolymers. The oligomers consist of only a few basic units, namely 2 to10.

Dialkyl aniline derivatives corresponding to general formula I: ##STR1##in which R₁ is a CH₃ or C₂ H₅ radical,

m is a number 0, 1 or 2,

A represents O, NH or ##STR2## X is a polymer of ethylene or propyleneoxide.

N,N-dimethyl derivatives and derivatives with substituents in the m- orp-position are advantageous.

The dialkyl aniline derivatives of formula I according to the inventionmay be prepared from N,N-dialkyl aniline compounds containing reactivegroups, such as OH, NH₂, CH₂ OH, ##STR3## or CH₂ NH₂, and suitablepolymerizable low molecular weight compounds, such as ethylene orpropylene oxide. Their molecular weight is preferably of the order of700.

Particularly preferred aniline derivatives correspond to general formulaII: ##STR4## in which R₁, m and A have the same meaning as in formula I,

n is a number of 1 to 6 and

Y is a group obtainable by reaction of n-functional isocyanate, epoxide,carboxylic acid, carboxylic acid ester or carboxylic anhydride compoundswith the substituents --AH of the N,N-dialkyl aniline group.Accordingly, these activators according to the invention are reactionproducts of reactive oligomers or prepolymers with correspondingfunctional tertiary amines. Examples of the functionality of theoligomers or polymers are isocyanate, epoxy, carboxyl, ester orcarboxylic anhydride groups. p-Dimethylaminobenzyl alcohol,3-dimethylaminophenol, N,N-dimethylamino-p-phenylene diamine andN,N-dimethylamino-m-phenylene diamine may be used as reactiveN,N-dialkyl aniline compounds.

In the production of the (poly)urethane-based activators, it is ofadvantage initially to react polyols, such as polyethylene glycol,polypropylene glycol, trimethylol propane, polycaprolactone andpolyoxytetramethylene, with diisocyanates and subsequently to react theproduct of this reaction with the N,N-dialkyl aniline derivativesbearing reactive substituents, such as --OH, --NH₂, --CH₂ OH, --CH₂ NH₂and --COOH.

The present invention also relates to a combination product for bondingparts to be joined which contains a cyanoacrylate adhesive in additionto the N,N-dialkyl derivatives according to the invention. Thecyanoacrylate adhesive consists essentially of monomeric cyanoacrylatescorresponding to the general formula H₂ C═C(CN)--COOR, where R is analkyl, alkenyl, cycloalkyl, aryl, alkoxyalkyl, aralkyl or haloalkylgroup, more particularly a methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, pentyl, hexyl, allyl, methallyl, crotyl, propargyl,cyclohexyl, benzyl, phenyl, cresyl, 2-chloroethyl, 3-chloropropyl,2-chlorobutyl, trifluoroethyl, 2-methoxyethyl, 3-methoxybutyl and2-ethoxyethyl group. The cyanoacrylates mentioned above are known to theexpert on adhesives, see Ullmann's Encyclopedia of Industrial Chemistry,Vol. A1, page 240, Verlag Chemie Weinheim (1985), and U.S. Pat. Nos.3,254,111 and 3,654,340.

The activators according to the invention have above all the followingpositive effects:

They can also act as a primer, i.e. increase bond strength afterpriming.

They enable the cure time to be adjusted under control which providesfor safe working.

They lead to transparent colorless bonds, i.e. the use of the activatorsaccording to the invention produces hardly any visible changes, such aswrinkling or white discoloration.

They have a good technical property profile comparable with that of theknown N,N-dimethyl toluidine.

The reduction in strength is negligible.

There is no evidence of any odor.

Toxicity is reduced.

EXAMPLES

The invention is illustrated by the following Examples.

I Starting Products

The activators according to the invention were prepared from thefollowing aniline compounds and reactive oligomers or prepolymers:p-Dimethylaminobenzyl alcohol I, 3-dimethylaminophenol II andN,N-dimethylamino-p-phenylenediamine III. ##STR5##

The oligomers or prepolymers are:

1. T1890/100 (trimerized isophorone diisocyanate, a product of Huls),

2. DESMODUR N (trimerized hexamethylene diisocyanate, a product of BayerAG),

3. Reaction product of TDI (2,4-toluene diisocyaante) and CP 455(macrotriol based on polypropylene glycol with a molecular weight ofapprox. 430) so that a product of the CP 455×3 TDI type if formed.

4. Reaction product of TDI (2,4-toluene diisocyanate) and TMP(trimethylol propane) so that a product of the TMP×3 TDI type is formed.

5. Reaction product of TDI (2,4-toluene diisocyanate) and PPG 425(difunctional polypropylene glycol) so that a product of the PPG 425×2TDI type is formed.

To prepare the NCO-terminated PUR's 3), 4) and 5), an approximately 20%solution of the polyol and the TDI in ethyl acetate was heated to 80° C.to reach the theoretical NCO content.

II Production of the Activators According to the Invention

A) Activator of the T 1890/100×3 II type

10.3 g 3-N,N-dimethylaminophenol (II) dissolved in 20.6 g ethyl acetatewere added to a solution of 18.3 g T 1890/100 (trimerized isophoronediisocyanate, a product of Huls) in 18.3 g ethyl acetate and the mixtureobtained was heated for 1 hour to the reflux temperature. After additionof 15 mg STANCLERE TL (dibutyl tin dilaurate), the mixture was kept atthe boiling temperature until the NCO content fell below 0.2%. Thesolution obtained was then diluted to the desired in-use concentration.The molecular was approx. 1,100.

B) Activator of the T 1890/100×3 III type

As in A), except that N,N-dimethylamino-p-phenylene diamine (III) wasused instead of 3-N,N-dimethylaminophenol (II). The molecular weight wasapprox. 1,100.

C) Activator of the T 1890/100×3 I type

As in A), except that p-N,N-dimethylaminobenzyl alcohol (I) was usedinstead of 3-N,N-dimethylaminophenol (II). The molecular weight wasapprox. 1,100.

D) Activator of the DESMODUR N×3×II type

As in A), except that DESMODUR (2) was used instead of T 1890/100 (1).The molecular weight was approx. 1,000.

E) Activator of the CP 455×3 TDI×3 I type

4-N,N-dimethylaminobenzyl alcohol (I) in the form of an approx. 20%solution in ethyl acetate was added at 60° C. to an approximately 20%solution of the reaction product of TDI and CP 455 (3) and the resultingsolution was heated at the reflux temperature until the NCO content wasbelow 0.05%. The solution thus obtained was diluted to the desiredin-use concentration. The molecular weight was approx. 1,400.

F) Activator of the TMP×3 TDI×3 I type

As in E), except that TMP was used instead of CP 455. The molecularweight was approx. 1,100.

G) Activator of the PPG 425×2 TDI×2 I type

As in E), except that the trifunctional prepolymer based on PPG wasreplaced by a difunctional prepolymer. The molecular weight was approx.1,100.

III The Activators were Tested According to the Following Criteria

a) reactivity,

b) cure rate on activated aluminium test strips,

c) cure rate after activation,

d) tensile shear strength on sand-blasted aluminium strips,

e) transparency and

f) odor of the activator.

a) Determination of reactivity

Degreased aluminium strips are immersed in an activator solution and,after airing of the solvent (2 minutes), were bonded to a non-activatedtest strip. The cyanoacrylate was applied to the untreated test strips.To determine reactivity, the test strips bonded with a 1.5 cm overlapare fixed for a certain time and loaded with a 500 g weight. Thereactivity is expressed as the time after which the bond can be loadedwith the weight for 5 seconds.

b) Cure rate on activated test strips

Degreased aluminium test strips are sprayed with the activator solutionsfrom a distance of approx. 15 cm. After airing (approx. 2 minutes), adrop and a bead are applied to the treated test specimens and the timeafter which the cyanoacrylate has completely polymerized is determined.

c) Cure rate on subsequently activated surfaces

A drop and a bead of cyanoacrylate adhesive are also applied todegreased aluminium test stips. Premature polymerization is obtained bysubsequent spraying with a 2% activator solution. In practice, this is amethod of curing excess adhesive.

d) Testing of tensile shear strength on sand-blasted aluminium strips

For this measurement, degreased sandblasted test strips are bonded witha 1 cm overlap. The test specimens are pretreated by immersion in theactivator solution. After evaporation of the solvent, the cyanoacrylateadhesive is applied to an untreated test strip because polymerizationwould take place immediately if it were applied to activated test strip,preventing accurate adjustment. The measurements were carried out afterstorage for 5 days at room temperature.

IV Test Results

With the cyanoacrylate adhesive SICOMET 8300 of Sichel-Werke GmbH (Basedon ethyl cyanoacrylate), the activators according to the inventionproduced the following results which were compared with those ofN,N-dimethyl toluidine (DMT):

The activators according to the invention have a far less unpleasantodor than DMT.

The appearance of the adhesive cured with the activators according tothe invention corresponds to that of the adhesive activated withdimethyl toluidine, particularly in regard to transparency.

Strength was slightly reduced, but remained at an acceptable level.

The activators according to the invention basically cure the adhesivemore slowly than dimethyl toluidine for the same concentration byweight.

Cure times on activated strips of basically less than 60 seconds areobserved in the case of a bead. This accords with the known activatorDMT. In the case of a drop, the cure time rises to 120 seconds andlonger whereas, with DMT, it increases to approx. 80 seconds. Similarresults are obtained where curing is followed by spray activation.

Some of the results obtained with a 1% by weight solution in ethylacetate are set out in the following Table:

    ______________________________________                                        Activator   Strength [n/mm.sup.2 ]                                                                     Reactivity [s]                                       ______________________________________                                        DMT         14.1         20                                                   E           10.4         35                                                   F           7.0          30                                                   C           14.8         30                                                   B           11.5         15                                                   A           13.4         15                                                   D           13.2         30                                                   ______________________________________                                    

The activators according to the invention provide for controlled curingbehavior: reactivity and cure time in seconds in the event of subsequentspray activation with a solution of activator A.

    ______________________________________                                                  Cure time (secs.)                                                   % by weight                                                                              Drop        Bead    Reactivity [s]                                 ______________________________________                                        0.2        >300        >300    45                                             0.5        >300        300     15                                             1.0        120         40      15                                             2.0        90          20      <15                                            ______________________________________                                    

We claim:
 1. A composition of matter useful for bonding parts to bejoined comprising a cyanoacrylate adhesive and an N,N-dialkyl anilinederivative having a molecular weight of more than 200 and at most 3carbon atoms for both N,N-dialkyl substituents together.
 2. Acomposition as claimed in claim 1 wherein said N,N-dialkyl anilinederivative has a molecular weight of more than
 600. 3. A composition asclaimed in claim 1 wherein said N,N-dialkyl aniline derivative has amolecular weight of about
 700. 4. A composition as claimed in claim 1wherein the N,N-dialkyl aniline group of said N,N-dialkyl anilinederivative is a terminal group of oligomers or polymers.
 5. Acomposition as claimed in claim 1 wherein said N,N-dialkyl anilinederivative has the following general formula: ##STR6## in which R₁ is aCH₃ or C₂ H₅ group,m is the number 0, 1 or 2, A represents O or NH orCOO and X is a polymer of ethylene or propylene oxide.
 6. A compositionas claimed in claim 1 wherein said N,N-dialkyl aniline derivative hasthe following general formula: ##STR7## in which R₁, m and A are asdefined in claim 3,n is a number of 1 to 6 and Y is a group obtainableby reaction of n-functional isocyanate, epoxide, carboxylic acid orcarboxylic anhydride compounds with the substituents--AH of theN,N-dialkyl aniline group.
 7. A composition as claimed in claim 6wherein the n-functional compounds contain the reaction products ofpolyethylene or polypropylene glycol.
 8. A composition as claimed inclaim 1 wherein said N,N-dialkyl aniline derivative is in the form of a0.1 to 5% by weight solution in an organic solvent.
 9. A composition asclaimed in claim 1 wherein said N,N-dialkyl aniline derivative is in theform of an impregnation of porous powders.